A standard urine test requires a sample free from outside contaminants for accurate diagnostic results. The purpose is to gather information about the urinary system and overall body health without interference. When menstruating, the presence of menstrual fluid may compromise the sample’s integrity. This contamination introduces substances not present in the urinary tract, potentially leading to misinterpretations.
How Menstrual Contamination Alters Results
Menstrual fluid interferes with a urine sample by introducing foreign materials as the urine passes through the vaginal area during collection. This fluid is a mix of blood, endometrial tissue, and cellular debris from the shedding uterine lining. Small contamination can skew the microscopic and chemical analysis performed by the laboratory.
The primary contaminants introduced are red blood cells (RBCs), white blood cells (WBCs), protein, and epithelial cells. These components are natural parts of menstrual discharge, but their presence makes it difficult to distinguish contamination from true pathology originating in the urinary tract. These substances can result in an “invalid” sample or the appearance of conditions that do not exist in the kidneys or bladder. High levels of RBCs from menstrual blood can mimic hematuria, which is blood originating from the urinary system.
The presence of WBCs and protein from menstrual fluid can lead to false positive findings for conditions like a UTI or kidney disease. Laboratories often note “squamous epithelial cells,” indicating the urine was contaminated from the external genital area. This analysis shows an abnormality not reflective of the body’s internal state.
Specific Effects on Common Urine Screenings
The consequences of menstrual contamination vary depending on the type of urine screening performed. For a routine urinalysis (UA), used to diagnose infections or kidney issues, contamination is a significant problem. Falsely elevated counts of RBCs, WBCs, and protein make it nearly impossible to accurately diagnose or rule out a UTI, bladder issue, or kidney pathology.
Contamination with WBCs can trigger a false positive result for the leukocyte esterase test, a common UA test for infection-fighting cells. This often requires the healthcare provider to order a more definitive test, such as a urine culture, or require a re-collection to confirm the diagnosis. Menstrual blood can also cause a false positive for the blood detection part of the test, creating concern for conditions like kidney stones.
For drug screenings, the effect of menstrual blood is generally less direct but remains a concern. While menstrual blood does not contain the drug metabolites these tests detect, heavy contamination can make the sample visually abnormal or alter its pH level. This may cause the sample to be flagged as “adulterated” or “invalid” by the collection facility, potentially requiring a retest and delaying results.
For pregnancy tests, heavy menstrual blood contamination typically does not interfere with the chemical detection of human chorionic gonadotropin (hCG). Excessive blood can physically obscure the test strip or cause administrative issues due to its visual appearance. Test timing relative to conception is usually a more significant factor than menstrual fluid.
Steps to Minimize Contamination During a Test
Minimizing contamination is possible even when a urine test cannot be postponed until after menstruation. Before collection, the individual should thoroughly cleanse the genital area from front to back using the antiseptic wipes provided by the facility. This technique helps remove bacteria and cellular debris that could otherwise enter the sample cup.
The most effective physical measure to prevent blood from entering the sample is to insert a fresh tampon or menstrual cup immediately before collection. This acts as a barrier to catch the flow of menstrual fluid, keeping it away from the urinary opening. If a tampon cannot be used, careful separation of the labia during urination is necessary.
The sample should be collected using the “clean catch” or “midstream” method. This involves starting the flow of urine into the toilet first. Then, place the collection cup into the stream to catch the mid-portion of the urine, and release the final portion into the toilet.
It is advisable to inform the collection facility or healthcare provider that menstruation is occurring before providing the sample. This communication allows the staff to correctly interpret any abnormal findings, such as the presence of blood or epithelial cells, due to the menstrual cycle. They may also advise rescheduling the test if it is not urgent or suggest an alternative collection method, such as a catheterized specimen, if a completely clean sample is necessary for accurate results.